Only you can know about the 1st house since its ur "doorstep" personality.Jupiter in 12th is good at fitting in anywhere. They don't look down on others and can be open to all(even shady characters).
This could also be their downfall i.e trusting others blindly or not looking into details etc. As this may result in them being taken advantage of by malevolent types.
Jupiter in 12th is also the type to be more forgiving of not only their own shortfalls, but the shortfalls of others. Maybe too forgiving.
Jupiter conjunct the 1st house also gives an optimistic outlook. You may not be the type to suffer from depression or be down for too long as Jupiter expands your views and diversifies.
So the Jupiter in 1st house is rarely without options. Tomorrow is filled with possibilities for these people. So worry and stress are short-lived.
The other thing is that you are someone who is at peace with how you look.
So insecurities about your height/weight etc. Are not the stuff of Jupiter. Jupiter is "above it all" and accepts that there may be others that are more beautiful or more attractive.
But they are not the type to be competitive and are more accepting of the fact that they may not be everyone's cup of tea. This is also refreshing. Because when Venus/Jupiter in 7th, there is a danger of trying to be the "be all" to everyone.
Jupiter/Venus in 1st or ruling the 1st has an innate belief in the goodness of life and their intrinsic ability to feel good.
It is that that makes them attractive, as I am not too fond to regurgitate the "Venus in 1st" is beautiful etc. Because this beauty is not always so much externally apparent (genetics do that).
But this beauty glows more internally. Like a jewel that is ageless because it is inextricably combined with character and is a joy to come into contact with.
If you relate to both, what was said above about the planet on the cusp affecting both houses may be true for you. How do you see yourself ?